Device and method for controlling drive test in wireless communication system

ABSTRACT

An apparatus and method for matching the radio channel measurement timing of Minimization of Drive Test (MDT) cycle with timings of the Discontinuous Reception (DRX) cycle are provided. The radio channel measurement method of a terminal according to the present invention includes configuring a DRX cycle, receiving a Minimization of Drive Test (MDT) cycle, comparing the DRX cycle and the MDT cycle, measuring, when the MDT cycle is an integer multiple of the DRX cycle, the radio channel at DRX timings matching with MDT timings, and storing a result of the measurement.

PRIORITY

This application claims the benefit under 35 U.S.C. §119(a) of a Koreanpatent application filed on Aug. 20, 2010 in the Korean IntellectualProperty Office and assigned Serial No. 10-2010-0080946, the entiredisclosure of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a Minimization of Drive Test (MDT)measurement device and method. More particularly, the present inventionrelates to a device and method for determining a measurement cycle of aradio channel measurement cycle for collecting radio channel informationto be used for optimization of a service area for a terminal operatingin standby mode.

2. Description of the Related Art

Typically, mobile communications have been developed for the user tocommunicate while moving. With the rapid advance of technologies, themobile communication system has evolved to a level capable of providinga high speed data communication service as well as a voice communicationservice. Recently, the 3^(rd) Generation Partnership Project (3GPP), asone of the next generation mobile communication standardizationorganizations, is in the progress of standardization of Long TermEvolution-Advanced (LTE-A). LTE-A is a high speed packet-basedcommunication technology supporting a data rate higher than that of thecurrent mobile communication technology under the objective to completethe standardization in late 2010.

With the evolvement of the 3GPP standard, many discussions are beingconducted for optimizing a radio network in addition to the effort forincreasing the data rate. In the initial radio network configuration oroptimization stage, a base station or a base station controller shouldcollect radio environment information related to its own cell coverage.This process is called Drive Test. The conventional drive test isperformed in such a way that an operator carries a test apparatus on avehicle while performing the measuring task repeatedly for a long time.The measurement result is used to configure the system parameters of thebase stations or base station controllers. Such a conventional drivetest increases total costs and time for optimizing and maintaining theradio networks.

In order to improve the radio environment analysis and manualconfiguration process while minimizing the number of times of the drivetest, research is being conducted under the title of Minimization ofDrive Test (MDT). MDT is characterized in that the terminal transfersthe radio channel measurement information to the base stationperiodically or in response to a specific event. The operation of theterminal transmitting the measured radio channel information and othersupplementary information to the base station is referred to as MDTmeasurement information report hereinafter. The terminal transmits thechannel measurement result immediately when it can communicate with thebase station or, if the communication with the base station isunavailable, retains the MDT measurement information for transmissionwhen it becomes possible to communicate with the base station afterward.The base station uses the MDT measurement information received from theterminal for optimization of the cell region. In LTE-A, the MDTmeasurement information reports are classified according to UserEquipment (UE) Radio Resource Control (RRC) state as shown in Table 1.

TABLE 1 RRC state of UE MDT measurement information report operationIdle mode Logging and deferred reporting Connected mode Immediatereporting

In Table 1, if the UE is in the state of having no communication with anevolved Node B (eNB), this means that the UE is in idle mode. Otherwise,if the UE is in the state of having communication with the eNB, thismeans that the UE is in connected mode. In case of MDT, since thechannel information measured by the UE is transmitted by RRC signaling,the UE in idle mode does not transition to the connected mode for theinformation transmission. Accordingly, the transmission of the channelmeasurement information is deferred until the UE transitions to theconnected mode. The UE collects the radio channel information at an MDTmeasurement interval in the connected mode or the idle mode. In order tomeasure the radio channel in idle mode, the UE has to turn on itsreceiver, resulting in power consumption. Accordingly, it is preferredto perform the MDT measurement and MDT report efficiently whileminimizing the power consumption of the UE.

SUMMARY OF THE INVENTION

Aspects of the present invention are to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages described below. Accordingly, an aspect of the presentinvention is to provide a method for performing Minimization of DriveTest (MDT) measurement efficiently in a mobile communication system.Accordingly, an aspect of the present invention is to provide a deviceand method for synchronizing the radio channel measurement interval witha Discontinuous Reception (DRX) cycle, especially when the UserEquipment (UE), in idle mode, measures the radio channel for collectingradio channel information to be used in service coverage optimization.

In accordance with an aspect of the present invention, a method for aterminal to measure a radio channel in a mobile communication system isprovided. The method includes configuring a DRX cycle, receiving an MDTcycle, comparing the DRX cycle and the MDT cycle, measuring, when theMDT cycle is an integer multiple of the DRX cycle, the radio channel atDRX timings matching with MDT timings, and storing a result of themeasurement.

In an exemplary implementation, an MDT server selects the terminal toperform MDT, determines the DRX cycle of the terminal, and sets the MDTcycle to an integer multiple of the DRX cycle.

In an exemplary implementation, the terminal measures, when the MDTcycle is not an integer multiple of the DRX cycle, the radio channel atMDT timings matching with DRX timings and stores a result of themeasurement and, at MDT timings mismatching with DRX timings, skipsmeasurement of the radio channel or records a last measurement result.

In an exemplary implementation, the terminal requests, when the MDTcycle is not an integer multiple of the DRX cycle, a base station toreset the MDT cycle to an integer multiple of the DRX cycle and receivesthe MDT cycle reset to the integer multiple of the DRX cycle.

In an exemplary implementation, the MDT server sets the MDT cycle to aninteger multiple of a maximum DRX cycle and notifies the terminal of theMDT cycle.

In accordance with another aspect of the present invention, a method forperforming Minimization of Drive Text (MDT) in a mobile communicationsystem is provided. The method includes setting, between a UserEquipment (UE) and a base station, a DRX cycle based on a UE-specificDRX cycle and a cell-specific DRX cycle, selecting, at an MDT server,the UE to measure a radio channel, requesting, at the MDT server, aMobility Management Entity (MME) for the DRX cycle of the UE,determining an integer multiple of the DRX cycle received from the MME,transmitting the integer multiple to the UE as the MDT cycle, andmeasuring, at the UE, the radio channel and storing a result of themeasurement at MDT timings matching with DRX timings.

In accordance with another aspect of the present invention, an apparatusfor measuring a radio channel in a mobile communication system isprovided. The apparatus includes a receiver for receiving a DRX cycle, acontroller including a cycle comparer for comparing the DRX cycle and aMinimization of Drive Text (MDT) cycle and an analysis/indication modulefor controlling, when the MDT cycle is an integer multiple of the DRXcycle, to measure the radio channel at DRX timings matching with MDTtimings, an MDT measurer measuring the radio channel under the controlof the controller, and a buffer buffering measurement of the radiochannel.

In an exemplary implementation, the mobile communication system includesan MDT server for selecting a terminal to perform MDT, for requestingthe base station for the DRX cycle of the selected terminal, forselecting an integer multiple of the DRX cycle as the MDT cycle, and fortransmitting the MDT cycle to the terminal.

In an exemplary implementation, the controller measures, when the MDTcycle is not an integer multiple of the DRX cycle, the radio channel atMDT timings matching with DRX timings and stores measurement result and,at MDT timings mismatching with DRX timings, skips measurement of theradio channel or records last measurement result without measuring theradio channel.

In an exemplary implementation, the controller requests, when the MDTcycle is not an integer multiple of the DRX cycle, a base station toreset the MDT cycle to an integer multiple of the DRX cycle and receivesthe MDT cycle reset to the integer multiple of the DRX cycle.

In an exemplary implementation, the mobile communication system includesan MDT server for setting, at an MDT server, the MDT cycle to an integermultiple of a maximum DRX cycle and for notifying the terminal of theMDT cycle.

Other aspects, advantages, and salient features of the invention willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainexemplary embodiments of the present invention will be more apparentfrom the following description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a diagram illustrating a standard control plane protocol stackin a Long Term Evolution (LTE) system according to an exemplaryembodiment of the present invention;

FIG. 2 is a diagram illustrating the concept of Signaling Radio Bearer(SRB) mapping in an LTE system according to an exemplary embodiment ofthe present invention;

FIG. 3 is a signaling diagram illustrating a Minimization of Drive Test(MDT) measurement for record and report procedure in standby modeaccording to an exemplary embodiment of the present invention;

FIG. 4 is a signaling diagram illustrating a procedure for determining aDiscontinuous Reception (DRX) cycle in an MDT method according to anexemplary embodiment of the present invention;

FIG. 5 is a signaling diagram illustrating a procedure for determining aDRX cycle and an MDT sampling cycle in an MDT method according to anexemplary embodiment of the present invention;

FIG. 6 is a signaling diagram illustrating a procedure for determiningan MDT sampling cycle according to a first exemplary embodiment of thepresent invention;

FIG. 7 is a diagram illustrating an MDT method for an exemplarysituation where the DRX cycle and the MDT sampling cycle mismatch witheach other according to a second exemplary embodiment of the presentinvention;

FIG. 8 is a diagram illustrating an MDT method for another exemplarysituation where the DRX cycle and the MDT sampling cycle mismatch witheach other according to the second exemplary embodiment of the presentinvention;

FIG. 9 is a flowchart illustrating an MDT measurement and recordingprocedure of a User Equipment (UE) in the MDT method according to thesecond exemplary embodiment of the present invention;

FIG. 10 is a signaling diagram illustrating a procedure for determiningthe MDT sampling cycle according to a third exemplary embodiment of thepresent invention;

FIG. 11 is a flowchart illustrating a method for determining an MDTsampling cycle at an evolved Node B (eNB) or an MDT server according toa fourth exemplary embodiment of the present invention;

FIG. 12 is a block diagram illustrating a configuration of a UEaccording to an exemplary embodiment of the present invention; and

FIG. 13 is a block diagram illustrating configurations of an eNB and anMDT server according to an exemplary embodiment of the presentinvention.

Throughout the drawings, it should be noted that like reference numbersare used to depict the same or similar elements, features, andstructures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of exemplaryembodiments of the invention as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the embodiments described hereincan be made without departing from the scope and spirit of theinvention. In addition, descriptions of well-known functions andconstructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of theinvention. Accordingly, it should be apparent to those skilled in theart that the following description of exemplary embodiments of thepresent invention is provided for illustration purpose only and not forthe purpose of limiting the invention as defined by the appended claimsand their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

Exemplary embodiments of the present invention propose a device andmethod for controlling a Minimization of Drive Test (MDT) measurementinterval in a 3^(rd) Generation Partnership Project (3GPP) system. Moreparticularly, exemplary embodiments of the present invention provide adevice and methods for synchronizing the radio channel measurementinterval with a Discontinuous Reception (DRX) interval, especially whena User Equipment (UE) in idle mode measures the radio channel forcollecting radio channel information to be used in service coverageoptimization.

The UE collects the radio channel information at an MDT measurementinterval while in connected mode or idle mode. Here, the radio channelinformation measurement can be periodical downlink pilot measurements.In order to collect the MDT measurement information in idle mode, the UEhas to activate its receiver, resulting in power consumption.Accordingly, by performing the MDT measurement according to a DRX cycle,it is possible to reduce the power consumption. The UE activates itsreceiver during the DRX period to decode the downlink control channel.Accordingly, if the MDT measurement cycle is synchronized with the DRXcycle, it is possible to negate the power consumption for activating thereceiver redundantly to perform the MDT measurement. In an exemplaryembodiment of the present invention, the MDT measurement cycle isconfigured to match with the DRX cycle or is configured in considerationof the DRX cycle. The MDT measurement information is transmitted to theeNB using the control plane protocol stack for processing the RadioResource Control (RRC) and Non-Access Stratum (NAS).

FIG. 1 is a diagram illustrating a standard control plane protocol stackin a Long Term Evolution (LTE) system according to an exemplaryembodiment of the present invention.

Referring to FIG. 1, the RRC layer 105 and 155 is responsible forcontrolling transmission of system information, RRC connection setup,and channel measurement operations. The Packet Data Convergence Protocol(PDCP) layer 110 and 150 is responsible for IP headercompression/decompression, and the Radio Link Control (RLC) layer 115and 145 is responsible for segmenting the PDCP Protocol Data Unit (PDU)into segments in appropriate size for Automatic Repeat Request (ARQ)operation. The Media Access Control (MAC) layer 120 and 140 isresponsible for establishing connection to a plurality of RLC entitiesso as to multiplex the RLC PDUs into MAC PDUs and demultiplex the MACPDUs into RLC PDUs. Each protocol layer entity adds an appropriateheader in need, i.e., the RLC layer 115 and 145 adds an RLC headerhaving a sequence number to an RLC Service Data Units (SDU), and the MAClayer 120 and 140 adds a MAC header having the RLC identifier to the MACSDU. The PHY layer 125 and 135 performs channel coding on the MAC PDUand modulates the MAC PDU into OFDM symbols to transmit over radiochannel 130 or performs demodulating and channel-decoding on thereceived OFDM symbols and delivers the decoded data to the higher layer.The PHY layer is responsible for Hybrid Automatic Retransmission Request(HARQ) operation of MAC PDUs. HARQ is a technique for retransmission onthe PHY layer and performing soft combining on the retransmitted packetsand initially transmitted packets.

FIG. 2 is a diagram illustrating the concept of Signaling Radio Bearer(SRB) mapping in an LTE system according to an exemplary embodiment ofthe present invention.

Referring to FIG. 2, the MDT measurement information recorded by the UEis delivered from the RRC layer 205 to the PDCP layer 230 via theSignaling Radio Bearer 2 (SRB2) 225. The RRC control message or NASmessage (dedicated control or NAS information) 210 is delivered via SRB0215, SRB1 220, or SRB2 225. SRB0 is used for delivering an RRC messageto be transmitted through a Common Control Channel (CCCH) 240 andassigned the highest priority. SRB 1 220 is used to deliver the RRCmessage to be transmitted through a Dedicated Control Channel (DCCH) 245and the NAS message is transmitted as piggybacked partially. SRB2 225 isused to deliver the NAS message through DCCH. The packets transmittedover the SRB1 220 and SRB2 225 are encoded through the integrity andciphering process 235. SRB1 220 has a higher priority than that of SRB2225. The MDT measurement information is transmitted over SRB2 225 havingthe lowest priority. In addition to SRB0 215 to SRB2 225, there existsData Radio Bearer (DRB) 250 for use in user plane data transmission. Thepacket to be transmitted over DRB 250 is delivered to the RLC layer 265through a ciphering and Robust Header Compression (ROHC) process 255,and the RLC layer 265 maps the packet to Dedicated Traffic Channel(DTCH) 260.

The UE in standby mode records the MDT measurement informationperiodically or when the measurement information fulfills a condition totrigger the MDT measurement information recording. The MDT measurementinformation recording events are as follows:

-   -   1. Periodical downlink pilot measurements    -   2. Serving cell becomes worse than threshold    -   3. Transmit power headroom becomes less than threshold

The periodical downlink pilot measurement is performed in order for theUE to measure and collect information for optimizing the service areaperiodically in the connected mode or the standby mode. The measurementis performed at an MDT measurement interval, and the eNB notifies the UEof the MDT configuration. In case that specific conditions arefulfilled, i.e. if the measured signal strength of the serving cell isequal to or less than the threshold value or if the transmit powerheadroom is equal to or less than the threshold value, the UE measuresand collects the information necessary for the optimization of theservice area. The MDT measure information recorded for service areaoptimization includes the following:

-   -   1. Global cell ID of a serving cell    -   2. Reference Signal Receive Power (RSRP) and Reference Signal        Receive Quality (RSRQ) measurement results of serving cell    -   3. Location information    -   4. Time stamp

The MDT measurement information should basically include the global cellID of the serving cell. This informs of the cell from which theinformation is collected. The global cell ID is the unique informationidentifying the cell. The radio channel condition of the serving cell(measurement results) can be expressed by a specific parameter. Theparameter can be RSRP or RSRQ in Evolved Universal Terrestrial RadioAccess (EUTRA), Received Signal Code Power (RSCP) Ec/No in EvolvedUniversal Mobile Telecommunications System (UMTS) Terrestrial RadioAccess Network (UTRAN), and Receive (Rx) level in Global System forMobile Communications (GSM)/Edge Radio Access Network (GERAN). Althoughthe description is directed to an EUTRA LTE system, exemplaryembodiments of the present invention can be applied to other types ofsystems. In 3GPP, the MDT function is expected to be applied to LTE andUMTS.

The location information (location info.) among the MDT measurementtransmitted to the eNB is an important factor. In case that it fails toacquire the location information based on a Global Positioning System(GPS), a set of the received signal strengths measured by the adjacenteNBs, and the set of the received signal strengths is referred to as aRadio Frequency (RF) fingerprint. The eNB that received the RFfingerprint is aware of the locations of the neighbor eNBs and canestimate the distances between the UE and neighbor cells with the signalstrength values of the neighbor cells using the signal propagationattenuation model. It is possible to locate the UE approximately usingthe triangulation method with the location information of the neighboreNBs and distances between the UE and the neighbor cells. In case thatthe GPS-based location information acquisition is impossible, it ispossible to transmit the information on the location estimated using theRF fingerprint to the eNB although it is not exact location information.

The time stamp is also important in the MDT measurement information. Thetime information is important for measuring the radio channel tooptimize the service area. This is because the radio channel conditionis time-varying. The time stamp is used effectively for reporting themeasurement information recorded in standby mode rather than reportingthe measurement information immediately in connected mode. Since themeasurement result is reported right after the measurement has completedin the connected mode, the time stamp is not so important. In thestandby mode, however, if no timestamp is used, it is impossible todetermine the time when the measurement has been performed. Accordingly,in the 3GPP standard under development, the time stamp is defined asmandatory information for the measurement report in standby modealthough not used in the immediate report.

The time stamp can be set to a value using different types. That is, theUE can set the time stamp to an absolute value or a relative value. Theabsolute value type requires a large number of bits to provide the timeinformation. In contrast, the relative value type requires a smallnumber of bits to provide the time information as compared to theabsolute value type. In order to reduce signaling overhead, the relativevalue type is used for the MDT measure information in the 3GPP standard.The eNB notifies the UE of the absolute time reference information, andthe UE inserts the relative time stamp into each measurement sample byreferencing the absolute time. When reporting the measurement result tothe eNB, the UE notifies of the absolute time provided by the eNBpreviously too. This is because the eNB which has provided the initialabsolute time reference information may differ from the eNB to which theUE is reporting currently.

FIG. 3 is a signaling diagram illustrating an MDT measurement for recordand report procedure in standby mode according to an exemplaryembodiment of the present invention. In the exemplary embodiment of FIG.3, it is assumed that the UE performs an MDT measurement and recodingoperation for measurement duration at an MDT sampling cycle and reportsthe measurement result to the eNB at two MDT sampling cycles.

Referring to FIG. 3, the eNB 305 transmits the MDT measurementconfiguration information to the UE 300 in connected mode in step 310.The MDT measurement configuration information includes the absolute timeinformation, MDT sampling cycle, and measurement duration. The absolutetime information is set as described above. The MDT sampling cycle isused for periodic downlink pilot signal measurement such that the radiochannel measurement is performed at the sampling cycle. The measurementduration is the total time for performing MDT. If the measurementduration expires, the UE stops MDT measurement.

If the RRC status of the UE transitions from the connected mode to thestandby mode in step 315, the UE starts MDT measurement. Here, the UEcollects and records the first MDT measurement sample in step 320. TheMDT measurement and recording is performed at the MDT sampling cycle325, notified at step 310, in steps 323, 350, and 353. The UE performsthe MDT measurement recording for every measurement sample, and theaforementioned MDT measurement information is recorded as denoted byreference numbers 330 to 333. The logged samples 330 to 333 can includethe aforementioned information, i.e. global cell ID, measurementresults, location information, and time stamp. Once the UE re-enters theconnected mode (connection recovery) at step 335, the UE notifies theeNB whether there are available recorded MDT measurement (indicationwhether or not there are available logs) in step 340. The eNB canrequest for the measurement report. Upon receipt of the measurementreport request, the UE reports the recorded MDT measurement and deletesthe recorded information. The recorded information is retained until themeasurement report request.

The UE enters the standby mode again in step 345 and, if the measurementduration is not expired yet, continues MDT measurement (connectionrelease and MDT start) to collect the MDT measurement information(measurement sample taken) in step 350. The measurement duration can beset with or without consideration of the time in the connected mode. Ifthe MDT measurement duration expires, the UE terminates MDT measurementin step 355. After terminating the MDT measurement, the UE re-enters theconnected mode (connection recovery) in step 360, and, in step 365,notifies the eNB of the MDT measurement information to be reported, andreports, if there is the measurement report request from the eNB, themeasurement result.

In case that the UE performs the MDT measurement and report of radiochannel information to be used for service area optimizationperiodically in the standby mode, it is preferred to synchronize the MDTsampling cycle with the DRX cycle. Discontinuous Reception is capable ofreducing power consumption caused by continuous monitoring on thedownlink control channel. DRX can be applied in both the connected andstandby modes and determines the time of paging to the UE. The eNB pagesthe UE periodically and thus the UE senses the paging signal on thedownlink control channel. Hereinafter, this interval is referred to asDRX cycle.

FIG. 4 is a signaling diagram illustrating a procedure for determining aDRX cycle in an MDT method according to an exemplary embodiment of thepresent invention.

Referring to FIG. 4, the UE 405 receives the SIB2 as the systeminformation message broadcast by the eNB 410 in step 420. The SIB2includes the default paging cycle information indicating thecell-specific DRX cycle. The default paging cycle can be set to a valueindicating one of 32, 64, 128, and 256 frames. Here, a frame has thelength of 10 ms and thus, if the paging cycle is 32 frames, this meansthat the DRX cycle is 32 ms. The eNB 405 transmits an attach requestmessage to the Mobility Management Entity (MME) 415 in the initial UEregistration process in step 425. The attach request message includesthe UE-specific DRX cycle. The specific DRX cycle also has a value ofone of 32, 64, 128, and 256 frames. The MME 415 transmits an attachresponse message to notify the UE of the completion of the UEregistration in step 430.

The UE 405 compares the default paging cycle value (cell-specific value)provided by the eNB 410 with the UE-recommended DRX (UE-specific value)to determine the smallest one of the cell-specific and UE-specificvalues as the DRX cycle in step 435. At this time, the MME 415 deliversthe DRX cycle received from the UE to the eNB 410 in step 440. Uponreceipt of the DRX cycle, the eNB 410 compares the default paging cyclevalue (cell-specific) with the UE-recommended DRX value (UE-specific) todetermine one of the cell-specific and UE-specific values as the DRXcycle in step 445. If it is necessary to page the UE 405, the eNB 410transmits the paging message at the determined DRX cycle in step 450.The UE 405 performs monitoring on the Physical Downlink Control Channel(PDCCH) to detect the paging message transmitted by the eNB 410 and, ifreceived, performs decoding on the paging message.

Here, the DRX cycle may differ from the MDT sampling cycle. This isbecause the MDT sampling cycle is determined by the MDT server. If theMDT sampling cycle is equal to the DRX cycle or an integer multiple ofthe DRX cycle, the MDT sampling cycle can be used as it is. However, theMDT sampling cycle may be less than the DRX cycle or not an integermultiple of the DRX cycle. The reason why the DRX cycle and the MDTsampling cycle may not match with each other is because the DRX and MDTsampling cycles are determined by different entities.

FIG. 5 is a signaling diagram illustrating a procedure for determining aDRX cycle and an MDT sampling cycle in an MDT method according to anexemplary embodiment of the present invention.

Referring to FIG. 5, the DRX cycle is determined with the involvement ofthe UE 505, the eNB 510, and the MME 515. However, the MDT samplingcycle is determined with the involvement of the UE 505, the eNB 510, andthe MDT server 520. The process for determining the DRX cycle in steps525 to 550 is identical with that of steps 420 to 445 of FIG. 4. Thatis, the UE 505 and eNB 510 compare the DRX cycles of the eNB 510 and UE505 to determine the DRX cycle having the value less than the other.

In the MDT sampling cycle determination process, the MDT server 520selects a UE to perform the MDT operation in step 555. The MDT servertransmits the MDT configuration information including the MDTmeasurement information to the eNB 510 in step 560. Here, the MDTconfiguration information includes the MDT sampling period. The eNBdelivers the MDT configuration information to the UE 505 to perform MDToperation in step 565. At this time, the MDT configuration can begenerated by the eNB 510.

Comparing the DRX cycle determination process and the MDT sampling cycledetermination process, it is noted that the two DRX and MDT samplingcycles are determined by different entities. In contrast to the DRXcycle which is determined by comparing the default paging cycle (orcell-specific DRX cycle) with the UE-recommended cycle (UE-specificcycle), the MDT sampling cycle is determined by the MDT server 520.Accordingly, it is unlikely that the MDT sampling cycle always matcheswith an integer multiple of the DRX cycle. For example, if the MDTsampling cycle is set to 64 while the DRX cycle is 128, the MDTmeasurement is performed at a timing different from the DRX timing.Accordingly when the MDT sampling cycle is less than the DRX cycle ornot an integer multiple of the DRX cycle, it is necessary to synchronizethe MDT sampling cycle with the DRX cycle. Descriptions are made ofexemplary methods for synchronizing the MDT sampling cycle and the DRXcycle hereinafter.

First Exemplary Embodiment

In a method for determining the MDT sampling cycle according to a firstexemplary embodiment of the present invention, the MDT server requeststhe MME for information on the DRX cycle of the UE for determining theMDT sampling cycle. The MDT server determines an integer multiple of theDRX cycle of the UE as the MDT sampling cycle.

FIG. 6 is a signaling diagram illustrating a procedure for determiningan MDT sampling cycle according to a first exemplary embodiment of thepresent invention.

Referring to FIG. 6, a UE 605, an eNB 610, and an MME 615 determine theDRX cycle through the procedure of FIG. 4 in step 625. Afterward, theMDT server 620 selects the UE 605 to perform MDT in step 630. The MDTserver 620 queries the MME 615 for the DRX cycle of the UE 605 in step635. In response to the query, the MME 615 notifies the MDT server 620of the DRX cycle of the UE 605 by transmitting a DRX cycle responsemessage in step 640. Once the DRX cycle of the UE 605 is determined, theMDT server 620 determines an integer multiple of the DRX cycle as theMDT sampling cycle in step 645. That is, the MDT server 620 determines avalue equal to the DRX cycle or an integer multiple of the DRX as theMDT sampling cycle. The MDT server 620 transmits the MDT configurationinformation including the MDT sampling cycle to the eNB 610 in step 650.The eNB 610 delivers the MDT configuration information to the UE 605 toperform MDT sampling in step 655.

Second Exemplary Embodiment

In a method for determining an MDT sampling cycle according to a secondexemplary embodiment of the present invention, the UE adjusts the MDTsampling cycle to match with the DRX cycle. As the simplest approach, ifthe MDT sampling cycle is shorter than or incompatible with the DRXcycle as a result of the comparison between the DRX cycle and MDTsampling cycle, the UE skips MDT measurement or reuses the most recentmeasurement result at the timings when two cycles mismatch with eachother. That is, when the MDT sampling cycle is shorter than or not equalto an integer multiple of the DRX cycle, the UE performs MDT measurementat the timings when the two cycles match with each other and skips MDTmeasurement or reuses the most recent measurement result at the timingswhen the two cycles mismatch with each other.

FIG. 7 is a diagram illustrating an MDT method for an exemplarysituation where the DRX cycle and MDT sampling cycle mismatch with eachother according to a second exemplary embodiment of the presentinvention.

Referring to FIG. 7, reference number 705 denotes the timings of a DRXcycle for the UE to sense the downlink control channel. Referencenumbers 710 and 715 denote the timings of the MDT sampling cycle. Asshown in FIG. 7, the MDT sampling cycle is shorter than the DRX cycle.Since the MDT sampling timings 710 match with the DRX timings 705, theUE performs MDT sampling at the timings 710. Meanwhile, the MDT samplingtimings 715 mismatch with the DRX timings 705. In this case, the UEskips MDT sampling and saves no record even when the MDT sampling timinghas arrived.

This approach can be applied to the case where the MDT sampling cycle islonger than or not compatible with the DRX cycle. For example, when theMDT sampling cycle is 1.5 times longer than the DRX cycle, the twocycles do not match completely with each other (i.e., not compatiblewith each other). In this case, the UE can perform and record the MDTsampling at the timings when the two cycles match with each other (atthe timings of the 3 multiple cycle of the DRX cycle) and skip the MDTsampling at the other MDT sampling timings. The method proposed in FIG.7 can be applied to cases where the MDT sampling cycle is shorter thanthe DRX cycle or the two cycles are not compatible with each other.

FIG. 8 is a diagram illustrating an MDT method for another exemplarysituation where the DRX cycle and the MDT sampling cycle mismatch witheach other according to the second exemplary embodiment of the presentinvention.

Referring to FIG. 8, the DRX cycle and the MDT sampling cycle areidentical with those depicted in FIG. 7, and the MDT sampling timings810 and 815 occur at a short interval as compared to the DRX timings805. At the MDT sampling timings 810 that match with the DRX timings805, the UE performs MDT measurement and records the measurement result.However, at the MDT sampling timings 815 when no DRX occurs, the UEskips MDT measurement operation. That is, even when the MDT samplingtiming has arrived, the UE skips the MDT sampling. Unlike the method ofFIG. 7, although not performing the MDT sampling, the UE records themost recent MDT measurement result at the MDT timings 815 mismatchingwith the DRX timings 810. Although there are redundant MDT measurementresult recordings, the method of FIG. 8 is advantageous to maintain theMDT sampling cycle instructed by the eNB.

Similar to the method of FIG. 7, the MDT measurement and recordingmethod described with reference to FIG. 8 can be applied to thesituations when the MDT sampling cycle is longer than the DRX cycle orincompatible with the DRX cycle since the MDT sampling cycle is not aninteger multiple of the DRX cycle.

In case that the MDT sampling is performed at a cycle different from theMDT sampling cycle notified by the MDT server as shown in FIGS. 7 and 8,the UE can report the actual MDT measurement cycle to the eNB or the MDTserver.

FIG. 9 is a flowchart illustrating an MDT measurement and recordingprocedure of a UE in the MDT method according to the second exemplaryembodiment of the present invention.

Referring to FIG. 9, the UE receives a default paging cycle on SIB2 fromthe eNB in step 905. The UE sends an attach request message including aDRX cycle in step 910. The UE sets its DRX cycle to min [default pagingcycle, UE-specific DRX cycle] in step 915. The UE receives theinformation necessary for the MDT measurement from the eNB in step 920.This information includes the MDT sampling cycle.

Once the DRX cycle and the MDT sampling cycle are determined, the UEdetermines whether the MDT sampling cycle is a multiple of the DRX cyclein step 925. If the MDT sampling cycle is equal to or a multiple of theDRX cycle, the UE performs MDT measurement in step 930 and records theMDT measurement result in step 935 at the MDT sampling cycle. If the MDTsampling cycle is equal to the DRX cycle, the UE performs the MDTmeasurement in synchronization with the DRX operation. And, if the MDTsampling cycle is twice longer than the DRX cycle, the UE performs theMDT measurement at every even numbered DRX timing (i.e., at an intervalof every two DRX timings). If the MDT sampling timing arrives, the UEperforms MDT measurement at step 930 and records the measurement results(logs the MDT measurement) at step 935.

Otherwise, if it is determined in step 925 that the MDT sampling cycleis not an integer multiple of the DRX cycle (i.e., the MDT samplingcycle is shorter than or not compatible with the DRX cycle), the UEdetermines whether the current MDT sampling timing matches with the DRXtiming in step 940. If the current MDT sampling timing matches with theDRX timing, the UE performs MDT measurement at step 930 and records themeasurement result at step 935. Otherwise, if the current samplingtiming does not match with the DRX timing (i.e., if the MDT samplingtiming is not identical with the DRX timing), the UE performs an MDTmethod according to one of the exemplary embodiments of FIGS. 7 and 8 instep 945. In case of using the method of FIG. 7, the UE skips the MDTmeasurement at the MDT timing. And, in case of using the method of FIG.8, the UE stores the latest MDT measurement as the current MDTmeasurement at the MDT timing. After either step 935 or step 945, the UEperforms step 950 by ending the exemplary procedure.

Third Exemplary Embodiment

In a method for determining the MDT sampling cycle according to a thirdexemplary embodiment of the present invention, the UE compares the MDTsampling cycle with the DRX cycle and reports, if the MDT sampling cycleis not an integer multiple of the DRX cycle (i.e., if the MDT samplingcycle is shorter than the DRX cycle or incompatible with the DRX cyclebecause it is not an integer multiple of, although longer than, the DRXcycle), an appropriate MDT sampling cycle is provided to the eNB so asto be assigned a new MDT sampling cycle.

FIG. 10 is a signaling diagram illustrating a procedure for determiningan MDT sampling cycle according to a third exemplary embodiment of thepresent invention.

Referring to FIG. 10, the UE 1005 receives the MDT configurationinformation from the eNB 1010 in step 1015. The MDT configurationinformation includes the MDT sampling cycle. The UE 1005 compares thereceived MDT sampling cycle with the DRX cycle in step 1020. If the MDTsampling cycle is shorter than the DRX cycle or incompatible with theDRX cycle (i.e., MDT sampling cycle is not an integer multiple of theDRX cycle), the UE 1005 sends the eNB 1010 the DRX cycle or arecommended MDT sampling cycle in step 1025. If a message carrying theDRX cycle or the recommended MDT sampling cycle is received, the eNB1010 forwards the message to the MDT server 1035 at step 1030. The MDTserver 1035 reselects the MDT sampling cycle having an appropriatedvalue based on the information contained in the received message at step1040. The MDT server 1035 sends the MDT configuration informationincluding the new MDT sampling cycle to the eNB 1010 at step 1045. TheeNB 1010 forwards the MDT configuration information including thereselected MDT sampling cycle to the UE 1005 in step 1050.

FIG. 10 shows an exemplary case where the MDT server 1035 determines theMDT sampling cycle. In a scenario where the eNB 1010 generates the MDTconfiguration information, however, the eNB 1010 can determine or changethe MDT sampling cycle. In this case, the eNB 1010 reselects the MDTsampling cycle based on the DRX cycle or the UE-recommended MDT samplingcycle received at step 1025 and informs the reselected MDT samplingcycle to UE 1005 and MDT server 1035.

Fourth Exemplary Embodiment

If the eNB or MDT server determining the MDT cycle needs the MDTmeasurement information recorded in a long period, it is possible tosend the UE an MDT sampling cycle determined in advance to match withthe DRX cycle. The DRX sampling cycle can be selected from a predefinedset of values. In an exemplary case of the LTE standard, one of 32, 64,128, and 256, which indicate a number frames, may be selected as the DRXcycle. If it is permitted to select the MDT sampling cycle longer thanthe longest DRX of 256 frames, the MDT sampling cycle can be set to avalue matching with the DRX cycle primarily. That is, if the MDTsampling cycle is set to a multiple of the maximum DRX cycle, there isno possibility for the MDT sampling cycle to mismatch with the DRX cycleof the UE.

FIG. 11 is a flowchart illustrating a method for determining an MDTsampling cycle at an eNB or an MDT server according to a fourthexemplary embodiment of the present invention.

Referring to FIG. 11, the eNB or the MDT server determining the MDTsampling cycle determines whether the required MDT sampling cycle islonger than the maximum DRX cycle at step 1105. If the MDT samplingcycle is long than the maximum DRX cycle, the MDT server sets the MDTsampling cycle to a value among the multiples of the maximum DRX cycleat step 1110. The eNB or the MDT server includes the MDT sampling cyclein the MDT configuration information at step 1115 and sends the MDTconfiguration information to the UE at step 1120.

Otherwise, if it is determined that the required MDT sampling cycle isequal to or shorter than the maximum DRX cycle at step 1105, the eNB orthe MDT server uses one of the above described methods (i.e., first tothird exemplary embodiments) to determine the MDT sampling cycle at step1130. After either step 1120 or step 1130, the eNB or the MDT serverperforms step 1125 by ending the exemplary procedure

FIG. 12 is a block diagram illustrating a configuration of a UEaccording to an exemplary embodiment of the present invention.

Referring to FIG. 12, a control unit 1205 is responsible for comparingthe MDT sampling cycle with the DRX cycle to adjust the MDT samplingcycle. The control unit 1205 includes a cycle comparer 1220 forcomparing the DRX cycle and the MDT sampling cycle and ananalysis/indication module 1225 for analyzing the comparison result. Thecycle comparer 1220 compares the DRX cycle and the MDT sampling cyclewith each other and sends the comparison result to theanalysis/indication module 1225. In case that the DRX cycle and the MDTsampling cycle differ from each other, the analysis/indication module1225 controls an MDT measurer 1235 of a transceiver 1210 and a buffer1215 in order to adjust the MDT sampling cycle. In this manner, theanalysis/indication module 1225 determines whether to perform the MDTmeasurement at the MDT measurement timing or requests the eNB for a newMDT sampling cycle. The transceiver 1210 includes an MDT configurationinformation receiver 1230 and the MDT measurer 1235. The MDTconfiguration information receiver 1230 receives the MDT configurationinformation from the eNB and forwards the MDT configuration informationto the control unit 1205. The MDT measurer 1235 performs MDT measurementunder the control of the control unit 1205. The buffer 1215 buffers themeasurement result of MDT performed by transceiver 1210.

In the MDT measurement and recording procedure of the above-structuredUE, the transceiver 1210 forwards the SIB2 message received from an eNBto the control unit 1205, and the control unit 1205 determines thedefault paging message or cell specific DRX cycle contained in the SIB2message. The control unit 1205 sets the DRX cycle to a smallest valueamong the default paging cycle and the UE-recommended DRX cycle. The MDTconfiguration information receiver 1230 of the transceiver 1210 receivesthe MDT configuration information transmitted by the eNB and forwardsthe MDT configuration information to the control unit 1205. The MDTconfiguration information includes the MDT sampling cycle.

The cycle comparer 1220 compares the DRX cycle and the MDT samplingcycle with each other and sends the comparison result to theanalysis/indication module 1225. The analysis/indication module 1225analyzes the comparison result and controls the MDT measurement andrecording based on the analysis result. The MDT measurement andrecording can be performed using one of the methods proposed in thefirst to fourth exemplary embodiments. In case that the MDT samplingcycle can be equal to or a multiple of the DRX sampling cycle, the MDTmeasurer 1235 performs DRX and MDT measurement at an interval equal toor a multiple of the DRX cycle. Otherwise, if the MDT sampling cycle isnot equal to or a multiple of the DRX sampling cycle (i.e., if the MDTsampling cycle is less than or incompatible with the DRX cycle), theanalysis/indication module 1225 controls the MDT measurer 1235 of thetransceiver 1210 to perform the MDT measurement according to one of theexemplary methods of FIGS. 7 and 8 and saves the measurement result inthe buffer 1215. In case that the MDT sampling cycle is not a multipleof the DRX cycle (i.e., the MDT sampling cycle is less than orincompatible with the DRX cycle), the analysis/indication unit 1225sends the UE's DRX cycle or the UE-recommended MDT sampling cycle to theeNB to receive a new MDT sampling cycle and control the MDT measurementand recording based on the new sampling cycle. At this time, the new MDTsampling cycle can be a multiple of the DRX cycle.

FIG. 13 is a block diagram illustrating configurations of an eNB and anMDT server according to an exemplary embodiment of the presentinvention.

Referring to FIG. 13, the eNB 1305 includes a controller 1315, atransceiver 1320, and a buffer 1325. The MDT server 1310 includes acontroller 1330 and a buffer 1335. An MDT measurement cycle controller1340 of the controller 1315 of the eNB 1305 receives the MDTconfiguration information from the MDT server 1310 and forwards the MDTconfiguration information to the UE by means of the transceiver 1320. Ifthere is the UE-recommended MDT sampling cycle, the MDT measurementcontroller 1340 sends the UE-recommended MDT sampling cycle to thecontroller 1330 of the MDT server 1310. The transceiver 1320 transmitsthe MDT configuration information to the UE by means of an MDTconfiguration information transmitter 1350 via the control channel andreceives the UE-recommended MDT sampling cycle from the UE. The buffer1325 of the eNB 1305 stores the MDT sampling information received fromthe UE temporarily before transmission to the buffer 1335 of the MDTserver 1310, and operates under the control of a buffer controller 1345of the controller 1315. The controller 1315 of the eNB 1305 controls thebuffer 1325 for transmission to the MDT server 1310.

The controller 1330 of the MDT server 1310 generates the MDTconfiguration information by means of an MDT sampling cycle analyzer1360 and provides the UE with the MDT configuration information. Thecontroller 1330 of the MDT server 1310 also analyzes the collected MDTmeasurement information to reconfigure the MDT configurationinformation. The buffer 1335 buffers the MDT measurement informationreceived from the UE via the eNB and operates under the control of abuffer controller 1365 of the MDT server controller 1330.

In the MDT sampling cycle determination procedure, the controller 1330of the MDT server 1310 selects a timing to perform the MDT measurementand determines the MDT sampling cycle of the selected UE. The controller1330 generates the MDT configuration information including the MDTmeasurement information and transmits the MDT configuration informationto the eNB 1305. The aforementioned operation can be performed by theMDT sampling cycle analyzer 1360.

The controller 1330 of the MDT server 1310 can determine the MDTsampling cycle according to the method proposed in the fourth exemplaryembodiment of the present invention. The controller 1330 determines thevalue of the maximum DRX cycle or an integer multiple of the DRX as theMDT sampling cycle. In this case, the MDT sampling cycle is set to amultiple of the DRX cycle of the selected UE.

Upon receipt of the MDT configuration information including the MDTsampling cycle, the controller 1315 of the eNB 1305 controls thetransceiver 1320 to transmit the received MDT configuration informationto the UE. That is, the MDT sampling cycle controller 1340 of thecontroller 1315 controls the MDT configuration information transmitter1350 to transmit the MDT configuration information received from the MDTserver 1310 to the UE.

In case that the MDT server 1310 determines the MDT sampling cyclewithout consideration of the DRX cycle of the UE, the MDT sampling cyclemay not be an integer multiple of the DRX cycle (i.e., the MDT samplingcycle is less than or incompatible with the DRX cycle). In this case,the UE can request a change of the MDT sampling cycle with thetransmission of a DRX cycle of the UE or the UE-recommended MDT samplingcycle as shown in FIG. 10. The transceiver 1320 of the eNB receives theMDT sampling cycle change request, and the MDT sampling cycle controller1340 of the controller 1315 forwards the request to the MDT server 1310.Upon receipt of the MDT sampling cycle change request, the controller1330 of the MDT server 1310 analyzes the DRX cycle of the UE or theUE-recommended MDT sampling cycle to determine a new MDT sampling cycle.Afterward, the controller 1330 transmits the MDT configurationinformation including the new MDT sampling cycle to the eNB 1305. Theaforementioned operation can be performed by the MDT sampling cycleanalyzer 1360 of the controller 1330.

Once the MDT sampling cycle is determined, the UE performs the MDTmeasurement and measurement result recording at the determined MDTsampling cycle. The MDT measurement result is recorded along with themeasurement time, and the measurement time can be the time of theexecution of MDT measurement in the form of relative or absolute time.The UE sends the recorded MDT measurement information to the eNB 1305 inconnected mode. The MDT measurement information receiver 1355 of the eNBtransceiver 1320 receives the MDT measurement information, and the MDTsampling cycle controller 1340 forwards the MDT measurement informationto the buffer controller 1345 such that the buffer controller 1345stores the MDT measurement information. The MDT sampling cyclecontroller 1340 sends the received MDT measurement information to theMDT server 1310. Upon receipt of the MDT measurement information, thebuffer controller 1330 of the MDT server 1310 stores the received MDTmeasurement information in the buffer 1335.

Although the description is directed to the case where the MDT samplingcycle is determined by the MDT server 1310, the MDT sampling cycle canbe determined by the eNB 1305.

In the following, DRX denotes a discontinuous reception interval, MDTcan be a radio channel measurement cycle, and the MDT server can be thechannel measurement server.

In the radio channel measurement cycle determination method for a mobilecommunication system according to an exemplary embodiment of the presentinvention, the UE determines the DRX cycle first and receives the MDTsampling cycle information from the eNB. Afterward, the UE compares theDRX cycle and the MDT sampling cycle with each other and, if the MDTsampling cycle is an integer multiple of the DRX cycle, synchronizes theMDT sampling cycle with the DRX cycle according to one of the methodsproposed in the second and third exemplary embodiments. The UE measuresthe radio channel and records the measurement records at the timings ofthe DRX cycle and the MDT sampling cycle.

At the timings when the MDT sampling cycle does not match with the DRXcycle, the UE skips measuring the radio channel and recording themeasurement result as described with reference to FIG. 7 or records thelatest measurement result as the current measurement result withoutmeasuring radio channel as described with reference to FIG. 8 in thesecond exemplary embodiment. Meanwhile, if the MDT sampling cycle is notan integer multiple of the DRX cycle, the UE transmits the DRX cycleinformation to the eNB, and the eNB resets the MDT sampling cycle withreference to the received DRX cycle information as described withreference to FIG. 10 in the third exemplary embodiment.

In case that the MDT sampling cycle is an integer multiple of the DRXcycle, the UE measures the radio channel and records the measurementresult at the MDT sampling cycle.

In the radio channel measurement cycle control method for a mobilecommunication system according to an exemplary embodiment of the presentinvention, the channel MDT server selects a UE to perform the MDTmeasurement, determines the MDT sampling cycle to be equal to an integermultiple of the DRX cycle of the selected UE, and transmits the MDTconfiguration information including the determined MDT sampling cycle tothe UE such that the UE performs the MDT measurement at the timings whenthe MDT sampling cycle matches with the DRX cycle.

The MDT sampling cycle determination of the MDT server can be performedin such a manner that the MDT server queries the MME for the DRX cycleand sets the MDT sampling cycle to a value equal to an integer multipleof the DRX cycle as described in the first exemplary embodiment withreference to FIG. 6. Also, it is possible to set the MDT sampling cycleto be a multiple of the DRX cycle as described in the fourth exemplaryembodiment with reference to FIG. 11.

As described above, an exemplary MDT control method of the presentinvention synchronizes the MDT sampling cycle at which the UE measuresthe radio channel for optimizing the service of the mobile terminal withthe DRX cycle of the UE in standby mode so as to minimize the number ofwakeups of the receiver of the UE, resulting in reduction of the powerconsumption of the UE.

While the invention has been shown and described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method for a terminal to measure a radiochannel in a mobile communication system, the method comprising:receiving a discontinuous reception (DRX) cycle from a base station;receiving a minimization of drive test (MDT) cycle; identifying whethera period for MDT measurement in the MDT cycle overlap with a DRX onduration in the DRX cycle; measuring, if the period for MDT measurementoverlap with the DRX on duration, the radio channel at the period forMDT measurement overlapping with the DRX on duration; and skipping, ifthe period for MDT measurement does not overlap with the DRX onduration, measurement of the radio channel.
 2. The method of claim 1,further comprising: selecting, at an MDT server, the terminal to performMDT; determining the DRX cycle of the terminal; and setting the MDTcycle to an integer multiple of the DRX cycle.
 3. The method of claim 1,further comprising: determining whether the MDT cycle is an integermultiple of the DRX cycle; measuring, when the MDT cycle is not aninteger multiple of the DRX cycle, the radio channel at the period forMDT measurement timings overlapping with DRX on duration and storing aresult of the measurement; and recording a last measurement result atthe period for MDT measurement not overlapping with the DRX on durationwithout measuring the radio channel.
 4. The method of claim 1, whereinthe identifying comprises: determining whether the MDT cycle is aninteger multiple of the DRX cycle; requesting, when the MDT cycle is notan integer multiple of the DRX cycle, the base station to reset the MDTcycle to an integer multiple of the DRX cycle; and receiving the MDTcycle reset to the integer multiple of the DRX cycle.
 5. The method ofclaim 1, further comprising: setting, at an MDT server, the MDT cycle toan integer multiple of a maximum DRX cycle; and notifying the terminalof the MDT cycle, wherein the MDT cycle is determined based on the DRXcycle by the MDT server.
 6. The method of claim 1, wherein the measuringthe radio channel comprises performing measurement of the radio channelat each of the periods for MDT measurement, if the MDT cycle is aninteger multiple of the DRX cycle.
 7. The method of claim 1, furthercomprising: storing a result of the measurement.
 8. The method of claim1, further comprising: determining whether the MDT cycle is an integermultiple of the DRX cycle; and measuring, if the MDT cycle is not aninteger multiple of the DRX cycle, the radio channel at the period forMDT measurement overlapping with the DRX on duration and storingmeasurement result.
 9. A method for performing minimization of drivetext (MDT) in a mobile communication system, the method comprising:setting, between a user equipment (UE) and a base station, adiscontinuous reception (DRX) cycle based on a UE-specific DRX cycle anda cell-specific DRX cycle; selecting, at an MDT server, the UE tomeasure a radio channel; requesting, at the MDT server, a mobilitymanagement entity (MME) for the DRX cycle of the UE; determining aninteger multiple of the DRX cycle received from the MME; transmittingthe integer multiple of the DRX cycle to the UE as the MDT cycle;measuring, at the UE, the radio channel at a period for MDT measurementin the MDT cycle overlapping with a DRX on duration in the DRX cycle andskipping the measuring, at the UE, the radio channel at the period forMDT measurement not overlapping with the DRX on duration; and storing aresult of the measurement, wherein the MDT cycle is determined based onthe DRX cycle by the MDT server.
 10. The method of claim 9, furthercomprising: setting, at the MDT server when the MDT cycle is longer thana maximum DRX cycle of the UE, the MDT cycle to an integer multiple ofthe maximum DRX cycle; and transmitting the MDT cycle to the UE.
 11. Themethod of claim 10, further comprising transmitting, when the UEconnects to the base station, the result of the measurement from the UEto the MDT server.
 12. An apparatus for measuring a radio channel in amobile communication system, the apparatus comprising: a transmitter forcommunicating with a base station; and a controller configured tocontrol to receive a discontinuous reception (DRX) cycle from the basestation, to receive a minimization of drive test (MDT) cycle, toidentify whether a period for MDT measurement in the MDT cycle overlapwith a DRX on duration in the DRX cycle, to measure, if the period forMDT measurement overlap with the DRX on duration, the radio channel atthe period for MDT measurement overlapping with the DRX on duration, andto skip, if the period for MDT measurement does not overlap with the DRXon duration, measurement of the radio channel.
 13. The apparatus ofclaim 12, wherein the mobile communication system comprises an MDTserver for selecting a terminal to perform MDT, for requesting the basestation for the DRX cycle of the selected terminal, for selecting aninteger multiple of the DRX cycle as the MDT cycle, and for transmittingthe MDT cycle to the terminal.
 14. The apparatus of claim 12, whereinthe controller is further configured to determine whether the MDT cycleis an integer multiple of the DRX cycle, to measure, when the MDT cycleis not an integer multiple of the DRX cycle, the radio channel at theperiod for MDT measurement overlapping with the DRX on duration andstores a result of the measurement and, to record a last measurementresult without measuring the radio channel at the period for MDTmeasurement not overlapping with the DRX on duration.
 15. The apparatusof claim 12, wherein the controller is further configured to determinewhether the MDT cycle is an integer multiple of the DRX cycle, torequest, when the MDT cycle is not an integer multiple of the DRX cycle,the base station to reset the MDT cycle to an integer multiple of theDRX cycle and to receive the MDT cycle reset to the integer multiple ofthe DRX cycle.
 16. The apparatus of claim 12, wherein the mobilecommunication system comprises an MDT server for setting, at the MDTserver, the MDT cycle to an integer multiple of a maximum DRX cycle andfor notifying the terminal of the MDT cycle, wherein the MDT cycle isdetermined based on the DRX cycle by the MDT server.
 17. The method ofclaim 12, wherein the controller is further configured to measure theradio channel at each of the periods for MDT measurement, when the MDTcycle is an integer multiple of the DRX cycle.
 18. The method of claim12, wherein the controller is further configured to store a result ofthe measurement.